Buying time when quakes hit

West Coast warning system could offer crucial seconds before destructive shaking begins

Students at Twin Lakes Elementary School in Federal Way, Wash., take shelter under tables in a 2012 earthquake drill. Millions of people took part in the “Great ShakeOut” to prepare for the possibility of real quakes in the future.

At 2:46 p.m. on March 11, 2011, an earthquake-detection station on Japan’s northeast coast began rocking back and forth, rattled by a powerful seismic wave racing from deep offshore. Just 5.4 seconds later, the Japan Meteorological Agency issued a notice that a magnitude 4.3 quake had begun.

As the seconds ticked by, however, and more stations picked up the rippling wave, the tremor started looking bigger. Three seconds after the first notice came an official warning: A quake of at least magnitude 7.2 was on its way. That’s a big tremor, even for earthquake-prone Japan. The city of Sendai needed to act quickly.

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